[PATCH v2] RISC-V: Check clint_time_val before use

[Anup Patel]

The NoMMU kernel is broken for QEMU virt machine from Linux-5.9-rc6
because the get_cycles() and friends are called very early from
rand_initialize() before CLINT driver is probed. To fix this, we
should check clint_time_val before use in get_cycles() and friends.

Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
for M-mode systems")
Signed-off-by: Anup Patel <anup.patel at wdc.com>
---
Changes since v1:
 - Explicitly initialize clint_time_val to NULL in CLINT driver to
   avoid hang on Kendryte K210
---
 arch/riscv/include/asm/timex.h    | 12 +++++++++---
 drivers/clocksource/timer-clint.c |  2 +-
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
index 7f659dda0032..6e7b04874755 100644
--- a/arch/riscv/include/asm/timex.h
+++ b/arch/riscv/include/asm/timex.h
@@ -17,18 +17,24 @@ typedef unsigned long cycles_t;
 #ifdef CONFIG_64BIT
 static inline cycles_t get_cycles(void)
 {
-	return readq_relaxed(clint_time_val);
+	if (clint_time_val)
+		return readq_relaxed(clint_time_val);
+	return 0;
 }
 #else /* !CONFIG_64BIT */
 static inline u32 get_cycles(void)
 {
-	return readl_relaxed(((u32 *)clint_time_val));
+	if (clint_time_val)
+		return readl_relaxed(((u32 *)clint_time_val));
+	return 0;
 }
 #define get_cycles get_cycles
 
 static inline u32 get_cycles_hi(void)
 {
-	return readl_relaxed(((u32 *)clint_time_val) + 1);
+	if (clint_time_val)
+		return readl_relaxed(((u32 *)clint_time_val) + 1);
+	return 0;
 }
 #define get_cycles_hi get_cycles_hi
 #endif /* CONFIG_64BIT */
diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
index d17367dee02c..8dbec85979fd 100644
--- a/drivers/clocksource/timer-clint.c
+++ b/drivers/clocksource/timer-clint.c
@@ -37,7 +37,7 @@ static unsigned long clint_timer_freq;
 static unsigned int clint_timer_irq;
 
 #ifdef CONFIG_RISCV_M_MODE
-u64 __iomem *clint_time_val;
+u64 __iomem *clint_time_val = NULL;
 #endif
 
 static void clint_send_ipi(const struct cpumask *target)
-- 
2.25.1